Dielectric ceramic composition and laminated ceramic capacitor

ABSTRACT

Problem It is difficult to secure the reliability of a laminated ceramic capacitor when the thickness of a dielectric ceramic layer is reduced to about 1 μm. Solving Means  
     The present invention provides a dielectric ceramic composition represented by the chemical composition formula: 100(Ba 1-x Ca x ) m TiO 3 +aMnO+bCuO+cSiO 2 +dRe 2 O 3  (wherein coefficients 100, a, b, c, and d each represent a molar ratio; and Re represents at least one element selected from Y, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, and Yb), wherein m, x, a, b, c, and d satisfy the respective relationships: 0.990≦m≦1.030, 0.04≦x≦0.20, 0.01≦a≦5, 0.05≦b≦5, 0.2≦c≦8, and 0.05≦d≦2.5.

TECHNICAL FIELD

The present invention relates to a dielectric ceramic composition and alaminated ceramic capacitor. In particular, the present inventionrelates to a dielectric ceramic composition and a laminated ceramiccapacitor capable of reducing the thickness of a dielectric ceramiclayer to about 1 μm.

BACKGROUND ART

Known dielectric ceramic compositions are proposed in, for example,Patent Documents 1, 2, 3, and 4.

Nonreducing dielectric porcelain compositions are proposed in PatentDocuments 1, 2, and 3. Basically, each of these nonreducing dielectricporcelain compositions principally contain 92.0 to 99.4 mol % of BaTiO₃,0.3 to 4 mol % of Re₂O₃ (Re represents at least one rare-earth elementselected from Th, Dy, Ho, and Er), and 0.3 to 4 mol % of Co₂O₃, andaccessorily contain 0.2 to 4 mol % of BaO, 0.2 to 3 mol % of MnO, and0.5 to 5 mol % of MgO.

Each of the nonreducing dielectric porcelain compositions can be firedwithout converting the structure into a semiconductor even under a lowoxygen partial pressure and has a dielectric constant of 3,000 or more,and an insulation resistance of 11.0 or more in terms of log IR.Furthermore, the temperature characteristics of the dielectric constantis within the range of ±15% over a wide temperature range of −55° C. to+125° C. with reference to a capacitance value at 25° C.

Furthermore, a dielectric ceramic composition and a laminated ceramiccapacitor are proposed in Patent Document 4. The dielectric ceramiccomposition principally contains barium titanate and accessorilycontains the following elements: Re (Re represents at least onerare-earth element selected from Y, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, andYb), Ca, Mg, and Si. The chemical composition formula of the dielectricceramic composition is represented by100Ba_(m)TiO₃+aReO_(3/2)+bCaO+cMgO+dSiO₂ (wherein the coefficients of100, a, b, c, and d represent molar ratios), wherein the coefficients100, a, b, c, and d satisfy the respective relationships: 0.990≦m≦1.030,0.5≦a≦6.0, 0.10≦b≦5.00, 0.010≦c≦1.000,and 0.05≦d≦2.00, respectively.

The dielectric ceramic composition has a dielectric constant of 3,000 ormore, meets the B characteristics of JIS and X7R characteristics of EIA,and has a long accelerated insulation resistance life under hightemperature and high voltage, thus resulting in excellent reliabilityeven when the thickness of the dielectric ceramic composition isreduced.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 5-9066 (claims and paragraph No. [0009])

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 5-9067 (claims and paragraph No. [0009])

Patent Document 3: Japanese Unexamined Patent Application PublicationNo. 5-9068 (claims and paragraph No. [0009])

Patent Document 4: Japanese Patent Application No. 2001-39765 (claimsand paragraph Nos. [0066] and [0067]).

In recent years, in the development of electronic technology, rapidprogress has been made in the miniaturization of electronic components,and trends toward miniaturization and higher capacities of laminatedceramic capacitors have become significant. However, conventionaldielectric ceramic compositions are designed on the premise that thecompositions are used under low field strength. As a result, the use ofa thin layer of the dielectric ceramic composition, i.e., the use of thedielectric ceramic composition under high field strength hasdisadvantages of significant reductions in insulation resistance,dielectric strength, and reliability. Therefore, when the thickness of aceramic dielectric layer is reduced in the conventional dielectricceramic composition, it is necessary to reduce the rated voltagedepending on the thickness.

In each of dielectric ceramic compositions proposed in Patent Documents1 to 4, it is possible to provide a laminated ceramic capacitor havingexcellent reliability by constituting a dielectric ceramic layercomposed of the dielectric ceramic composition. However, when thethickness of the dielectric ceramic layer is reduced to about 1 μm, itis disadvantageously difficult to secure the reliability of theresulting laminated ceramic capacitor.

The present invention is accomplished to overcome the above-describedproblems. It is an object of the present invention to provide adielectric ceramic composition and a laminated ceramic capacitor havinga high dielectric constant of 3,000 or more, a small dielectric loss of5% or less, a temperature characteristic of the dielectric constantmeeting the B properties (the rate of change of capacitance withreference to a capacitance at 20° C. is within the range of ±10% between−25° C. to +85° C.), a high resistivity of 10¹¹ Ωm or more, and highreliability, i.e., a mean failure time of 100 hours or more in anaccelerated reliability test (150° C., DC field strength: 10 V/μm), evenwhen the thickness of the dielectric ceramic layer is reduced to about 1μm.

DISCLOSURE OF INVENTION

According to a first aspect of the present invention, in a dielectricceramic composition represented by a chemical composition formula:100(Ba_(1-x)Ca_(x))_(m)TiO₃+aMnO+bCuO+cSiO₂+dRe₂O₃ (wherein coefficients100, a, b, c, and d each represent a molar ratio; and Re represents atleast one element selected from Y, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, andYb), m, x, a, b, c, and d satisfy the respective relationships:0.990≦m≦1.030, 0.04≦x≦0.20, 0.01≦a≦5, 0.05≦b≦5, 0.2≦c≦8, and 0.05≦d≦2.5.

According to a second aspect of the present invention, a laminatedceramic capacitor includes a plurality of laminated dielectric ceramiclayers; internal electrodes, each being disposed between dielectricceramic layers; and external electrodes electrically connected to therespective internal electrodes, wherein the dielectric ceramic layersare composed of the dielectric ceramic composition according to thefirst aspect.

According to a third aspect of the present invention, each of theinternal electrodes in the laminated ceramic capacitor according to thesecond aspect is composed of at least one conductive material selectedfrom nickel, a nickel alloy, copper, and a copper alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a laminated ceramic capacitoraccording to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below with reference to FIG. 1.For example, as shown in FIG. 1, a laminated ceramic capacitor 1 in thisembodiment includes a plurality of dielectric ceramic layers 2 (5 layersin this embodiment); a laminate containing a plurality of first internalelectrodes 3A and a plurality of second internal electrodes 3B, each ofthe first internal electrodes 3A being disposed between the dielectricceramic layers 2, and each of the second internal electrode 3B beingdisposed between the dielectric ceramic layers 2; and a first externalelectrode 4A disposed at one end of the laminate and electricallyconnected to the first internal electrode 3A, and a second externalelectrode 4B disposed at the other end of the laminate and electricallyconnected to the second internal electrode 3B.

As shown in FIG. 1, the first internal electrode 3A extends from one endof the dielectric ceramic layer 2 (left end in FIG. 1) to the vicinityof the other end (right end), and the second internal electrode 3Bextends from the right end of the dielectric ceramic layer 2 to thevicinity of the left end. The first and second internal electrodes 3Aand 3B are each composed of a conductive material. Any one of basemetals selected from nickel, nickel alloys, copper, copper alloys, andthe like can be preferably used as the conductive material. Furthermore,to prevent the structural defects in the internal electrodes, a smallamount of a ceramic powder may be incorporated in the conductivematerial.

As shown in FIG. 1, the first external electrode 4A is electricallyconnected to the first internal electrode 3A in the laminate, and thesecond external electrode 4B is electrically connected to the secondinternal electrode 3B in the laminate. Each of the first and secondexternal electrodes 4A and 4B may be composed of any one of variousknown conductive materials, such as Ag, Pd, alloys of Ag and Pd, andcopper. Each of the first and second external electrodes 4A and 4B maybe appropriately formed by a known process.

Each of the dielectric ceramic layers 2 is composed of a dielectricceramic composition according to this embodiment. This dielectricceramic composition is a composite oxide represented by the followingchemical composition formula:100(Ba_(1-x)Ca_(x))_(m)TiO₃+aMnO+bCuO+cSiO₂+dRe₂O₃. The coefficients,i.e., 100, a, b, c, and d, of the components of the dielectric ceramiccomposition each represent a molar ratio. Re represents at least onerare-earth element selected from V, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, andYb. Furthermore, m, x, a, b, c, and d in the chemical compositionformula satisfy the respective relationships: 0.990≦m≦1.030,0.04≦x≦0.20, 0.01≦a≦5, 0.05≦b≦5, 0.2≦c≦8, and 0.05≦d≦2.5.

(Ba_(1-x)Ca_(x))_(m)TiO₃ is a compound in which Ba ions in bariumtitanate are partially replaced with Ca ions. A substitution rate x ofCa ions to Ba ions less than 0.04 (substitution rate: 4%) is notpreferable because the mean failure time in a high-temperature load testis shorter than 100 hours. A substitution rate x exceeding 0.20(substitution rate: 20%) is also not preferable because the dielectricconstant is lower than 3,000, and the rate of change of the dielectricconstant with respect to temperature is disadvantageously outside therange of ±10%. A ratio of Ba_(1-x)Ca_(x) to Ti (m=Ba_(1-x)Ca_(x)/Ti)less than 0.990 is not preferable because the resistivity is lower than10¹¹ Ωm. The ratio m exceeding 1.030 is also not preferable because thedielectric constant is lower than 3,000, the rate of change of thedielectric constant with respect to temperature is disadvantageouslyoutside the range of ±10%, and the mean failure time is reduced.

A molar ratio a of MnO less than 0.01 relative to 100 of(Ba_(1-x)Ca_(x))_(m)TiO₃ is not preferable because the resistivity islower than 10¹¹ Ωm. A molar ratio a exceeding 5 is also not preferablebecause the rate of change of the dielectric constant with respect totemperature is disadvantageously outside the range of ±10%, and theresistivity is lower than 10¹¹ Ωm.

A molar ratio b of CuO less than 0.05 is not preferable because the meanfailure time is shorter than 100 hours. A molar ratio b exceeding 5 isalso not preferable because the rate of change of the dielectricconstant with respect to temperature is disadvantageously outside therange of ±10%.

A molar ratio c of SiO₂ less than 0.2 is not preferable because thedielectric constant is lower than 3,000, the dielectric loss tan δ ishigher than 5%, the rate of change of the dielectric constant withrespect to temperature is disadvantageously outside the range of ±10%,and the mean failure time is shorter than 100 hours. A molar ratio cexceeding 8 is also not preferable because the rate of change of thedielectric constant with respect to temperature is disadvantageously 10%or more, and the mean failure time is shorter than 100 hours.

A molar ratio d of Re₂O₃ less than 0.05 is not preferable because themean failure time is shorter than 100 hours. A molar ratio d exceeding2.5 is also not preferable because the rate of change of the dielectricconstant with respect to temperature is disadvantageously outside therange of ±10%. When a plurality of types of rare-earth elements Re arecontained, the total of molar ratios of the plurality of types of therare-earth elements Re is defined as d.

The process for producing a material powder used in the dielectricceramic composition is not particularly limited, and any productionprocess can be employed as long as the compound represented by(Ba_(1-x)Ca_(x))_(m)TiO₃ can be realized.

For example, the compound represented by (Ba_(1-x)Ca_(x))_(m)TiO₃ can beproduced by a step of mixing BaCO₃, TiO₂, and CaCO₃ and then a step ofreacting BaCO₃, TiO₂, and CaCO₃ by heat treatment.

The material powder of the dielectric ceramic composition can beproduced by a step of mixing the compound represented by(Ba_(1-x)Ca_(x))_(m)TiO₃ and oxides of Mn, Cu, Si, and Re (wherein Rerepresents at least one rare-earth element selected from Y, Sm, Eu, Gd,Th, Dy, Ho, Er, Tm, and Yb), which are additional components.

Furthermore, examples of the production process of the compoundrepresented by (Ba_(1-x)Ca_(x))_(m)TiO₃ include hydrothermal synthesis,hydrolysis, and wet synthesis such as a sol-gel method.

The starting materials of Mn, Cu, Si, Re (wherein Re represents at leastone rare-earth element selected from Y, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm,and Yb), which are additional components, are not limited to powderyoxides as long as a dielectric ceramic according to the presentinvention can be produced. A carbonate or a solution of an alkoxide, anorganometallic compound, or the like may be used. There is nodeterioration of the characteristics obtained by using these materials.

Such material powders are fired to produce the above-describeddielectric ceramic composition.

By using the above-described dielectric ceramic composition, it ispossible to produce a laminated ceramic capacitor having a highdielectric constant of 3,000 or more, a small dielectric loss of 5% orless, a temperature characteristic of the dielectric constant meetingthe B properties (within ±10%), a high resistivity of 10¹¹ Ωm or more,and high reliability, i.e., a mean failure time of 100 hours or more inan accelerated reliability test (high-temperature load test), even whenthe thickness of the dielectric ceramic layer is reduced to about 1 μm.Therefore, it is possible to produce a laminated ceramic capacitor inwhich the rated voltage need not be reduced even when the thickness ofthe dielectric ceramic layer is reduced to about 1 μm, the laminatedceramic capacitor being capable of achieving further miniaturization andhigher capacitances in the future.

Furthermore, in the laminated ceramic capacitor in this embodiment, theinternal electrode can be composed of a base metal, such as nickel, anickel alloy, copper, or a copper alloy, because the laminated ceramiccapacitor can be fired in a reducing atmosphere.

The present invention will be described below on the basis of specificexamples.

EXAMPLE 1

In this example, after preparing the material powder of a dielectricceramic composition, a laminated ceramic capacitor was produced with thematerial powder. First, highly pure TiO₂, BaCO₃, and CaCO₃, which werestarting materials, were prepared. These starting materials were weighedin a manner such that Ti, Ba, and Ca were contained in amountsrepresented by samples A to N shown in Table 1 and then were mixed andpulverized to produce powders. These powders were dried and then heatedat 1,000° C. or more to synthesize (Ba,Ca)TiO₃ material powders havingcompositions represented by samples A to N shown in Table 1 and eachhaving an average particle size of 0.20 μm. In addition, a CuO powder,an MnCO₃ powder, an SiO₂ powder, and an Re₂O₃ powder (wherein Rerepresents at least one rare-earth element selected from Y, Sm, Eu, Gd,Th, Dy, Ho, Er, Tm, and Yb), which were other material powders, wereprepared. In Table 1, asterisk-marked powders A to D were powders inwhich x and m were outside the range of the present invention. TABLE 1(Ba_(1−x)Ca_(x))_(m)TiO₃ Powder x m *A 0.038 1.003 *B 0.22 1.005 *C 0.080.988 *D 0.10 1.032 E 0.08 1.001 F 0.042 1.001 G 0.05 1.011 H 0.08 1.004I 0.14 1.007 J 0.17 1.02 K 0.19 1.005 L 0.08 0.992 M 0.08 1.015 N 0.081.027

Subsequently, the powders were weighed in a manner such thatcompositions shown in Tables 2 and 3 were achieved, and then mixed toobtain mixtures represented by sample Nos. 1 to 69. Then, these mixtureswere calcined in the range of 1,000° C. to 1050° C. for 2 hours toobtain calcines. A polyvinyl butyral binder and an organic solvent suchas ethanol were added to each calcine, and the resulting mixtures werewet-mixed with ball mills to prepare ceramic slurries. Each of theresulting ceramic slurries was formed into a sheet form by a doctorblade method to obtain a rectangular ceramic green sheet having athickness of 1.4 μm. Next, a conductive paste principally composed ofnickel (Ni) was applied onto each of the. resulting ceramic green sheetsby printing to provide a conductive paste film for forming an internalelectrode. One end of the conductive paste film is disposed at a firstend of the ceramic green sheet, and the other end of the conductivepaste film was disposed away from a second end of the ceramic greensheet. In Table 2, asterisk-marked sample Nos. 1 to 12 were samples inwhich any one of x, m, a, b, c, and d was outside the limited range ofthe present invention. TABLE 2 100 (Ba_(1−x)Ca_(x))_(m)TiO₃ + aMnO +bCuO + cSiO₂ + dRe₂O₃ Rare-earth Powder Sample element used x m a b c d*No. 1 Y A 0.038 1.003 0.200 0.400 2.00 0.5 *No. 2 Y B 0.22 1.005 0.2000.400 2.00 0.5 *No. 3 Y C 0.08 0.988 0.200 0.400 2.00 0.5 *No. 4 Y D0.10 1.032 0.200 0.400 2.00 0.5 *No. 5 Y E 0.08 1.001 0.005 0.400 2.000.5 *No. 6 Y E 0.08 1.001 5.200 0.400 2.00 0.5 *No. 7 Y E 0.08 1.0010.200 0.04 2.00 0.5 *No. 8 Y E 0.08 1.001 0.200 5.300 2.00 0.5 *No. 9 YE 0.08 1.001 0.200 0.400 0.10 0.5 *No. 10 Y E 0.08 1.001 0.200 0.4008.20 0.5 *No. 11 Y E 0.08 1.001 0.200 0.400 2.00 0.04 *No. 12 Y E 0.081.001 0.200 0.400 2.00 2.6  No. 13 Y F 0.042 1.001 0.200 0.400 2.00 0.5 No. 14 Y G 0.05 1.011 0.200 0.400 2.00 0.5  No. 15 Y H 0.08 1.004 0.2000.400 2.00 0.5  No. 16 Y I 0.14 1.007 0.200 0.400 2.00 0.5  No. 17 Y J0.17 1.02 0.200 0.400 2.00 0.5  No. 18 Y K 0.19 1.005 0.200 0.400 2.000.5  No. 19 Y L 0.08 0.992 0.200 0.400 2.00 0.5  No. 20 Y M 0.08 1.0150.200 0.400 2.00 0.5  No. 21 Y N 0.08 1.027 0.200 0.400 2.00 0.5  No. 22Y E 0.08 1.001 0.012 0.400 2.00 0.5  No. 23 Y E 0.08 1.001 0.100 0.4002.00 0.5  No. 24 Y E 0.08 1.001 0.400 0.400 2.00 0.5  No. 25 Y E 0.081.001 0.700 0.400 2.00 0.5  No. 26 Y E 0.08 1.001 1.000 0.400 2.00 0.5 No. 27 Y E 0.08 1.001 2.000 0.400 2.00 0.5  No. 28 Y E 0.08 1.001 3.5000.400 2.00 0.5  No. 29 Y E 0.08 1.001 4.800 0.400 2.00 0.5  No. 30 Y E0.08 1.001 0.200 0.055 2.00 0.5  No. 31 Y E 0.08 1.001 0.200 0.100 2.000.5  No. 32 Y E 0.08 1.001 0.200 0.700 2.00 0.5  No. 33 Y E 0.08 1.0010.200 1.000 2.00 0.5  No. 34 Y E 0.08 1.001 0.200 2.500 2.00 0.5  No. 35Y E 0.08 1.001 0.200 4.700 2.00 0.5

TABLE 3 100 (Ba_(1−x)Ca_(x))_(m)TiO₃ + aMnO + bCuO + cSiO₂ + dRe₂O₃Rare- Pow- earth der Sample element used x m a b c d No. 36 Y E 0.081.001 0.200 0.400 0.25 0.5 No. 37 Y E 0.08 1.001 0.200 0.400 0.50 0.5No. 38 Y E 0.08 1.001 0.200 0.400 1.00 0.5 No. 39 Y E 0.08 1.001 0.2000.400 4.00 0.5 No. 40 Y E 0.08 1.001 0.200 0.400 6.00 0.5 No. 41 Y E0.08 1.001 0.200 0.400 7.80 0.5 No. 42 Y E 0.08 1.001 0.200 0.400 2.000.055 No. 43 Y E 0.08 1.001 0.200 0.400 2.00 0.2 No. 44 Y E 0.08 1.0010.200 0.400 2.00 0.7 No. 45 Y E 0.08 1.001 0.200 0.400 2.00 1 No. 46 Y E0.08 1.001 0.200 0.400 2.00 2 No. 47 Y E 0.08 1.001 0.200 0.400 2.002.45 No. 48 Sm E 0.08 1.001 0.200 0.400 2.00 0.5 No. 49 Sm E 0.08 1.0010.200 0.400 2.00 1.5 No. 50 Eu E 0.08 1.001 0.200 0.400 2.00 0.5 No. 51Eu E 0.08 1.001 0.200 0.400 2.00 1.5 No. 52 Gd E 0.08 1.001 0.200 0.4002.00 0.5 No. 53 Gd E 0.08 1.001 0.200 0.400 2.00 1.5 No. 54 Tb E 0.081.001 0.200 0.400 2.00 0.5 No. 55 Tb E 0.08 1.001 0.200 0.400 2.00 1.5No. 56 Dy E 0.08 1.001 0.200 0.400 2.00 0.5 No. 57 Dy E 0.08 1.001 0.2000.400 2.00 1.5 No. 58 Ho E 0.08 1.001 0.200 0.400 2.00 0.5 No. 59 Ho E0.08 1.001 0.200 0.400 2.00 1.5 No. 60 Er E 0.08 1.001 0.200 0.400 2.000.5 No. 61 Er E 0.08 1.001 0.200 0.400 2.00 1.5 No. 62 Tm E 0.08 1.0010.200 0.400 2.00 0.5 No. 63 Tm E 0.08 1.001 0.200 0.400 2.00 1.5 No. 64Yb E 0.08 1.001 0.200 0.400 2.00 0.5 No. 65 Yb E 0.08 1.001 0.200 0.4002.00 1.5 No. 66 Y, Gd E 0.08 1.001 0.200 0.400 2.00 0.25 each  No. 67 Y,Gd E 0.08 1.001 0.200 0.400 2.00   1 each No. 68 Dy, Yb E 0.08 1.0010.200 0.400 2.00 0.5 each No. 69 Dy, Yb E 0.08 1.001 0.200 0.400 2.000.5 each

Next, a plurality of the ceramic green sheets that were the same typewere stacked in a manner such that the first end, in which theconductive paste films were disposed, and the second end werealternately disposed. The resulting stack was interposed between ceramicgreen sheets each having no conducting paste film and then was subjectedto press bonding to obtain a laminate. The resulting laminate was heatedto 350° C. in an N₂ atmosphere to decompose the binder and then firedfor 2 hours in a reducing atmosphere containing an H₂ gas, an N₂ gas,and an H₂O gas and having an oxygen partial pressure of 10⁻⁹ to 10⁻¹²MPa at the temperature shown in Tables 4 and 5. TABLE 4 Rate of changeof Firing Dielectric Dielectric loss dielectric constant Resistivitytemperature constant tan δ with temperature Log ρ Mean failure timeSample (° C.) (ε_(r)) (%) (%) (ρ:Ωm) (hour) *No. 1 1150 3420 4.1 −7.111.5 20 *No. 2 1150 2700 4.2 −11.1 11.5 40 *No. 3 1150 3200 3.5 −7.5 9.3Unmeasurable *No. 4 1150 2400 12.5 −12.8 9.5 Unmeasurable *No. 5 11503100 4.3 −9.4 9.4 Unmeasurable *No. 6 1100 3280 5.8 −12.1 10.5 20 *No. 71250 3310 4.4 −7.2 11.5 10 *No. 8 1150 3380 4.1 −12.3 11.4 150 *No. 91150 2400 7.8 −12.5 9.5 15 *No. 10 1150 3250 4.1 −11.8 11.5 40 *No. 111150 3250 4.2 −6.5 11.3 5 *No. 12 1150 3600 4.8 −11.2 11.2 120 No. 131150 3450 4.4 −7.5 11.4 110 No. 14 1150 3500 4.7 −7.2 11.3 140 No. 151150 3620 4.8 −6.9 11.4 170 No. 16 1150 3400 4.1 −6.1 11.2 230 No. 171150 3210 3.7 −8.5 11.3 150 No. 18 1150 3150 3.4 −9.1 11.5 115 No. 191150 3210 3.8 −7.8 11.1 110 No. 20 1150 3150 3.7 −8.5 11.3 130 No. 211150 3200 3.4 −8.9 11.5 140 No. 22 1150 3230 4.2 −5.4 11.1 115 No. 231150 3300 4.1 −6.1 11.3 120 No. 24 1150 3310 3.7 −5.8 11.5 140 No. 251150 3250 3.6 −5.7 11.3 160 No. 26 1125 3380 3.6 −6.5 11.1 175 No. 271125 3250 3.3 −7.8 11.4 200 No. 28 1100 3280 3.1 −8.8 11.5 170 No. 291100 3300 3.2 −9.4 11.4 120 No. 30 1150 3100 3.8 −8.1 11.3 105 No. 311150 3280 3.2 −7.5 11.1 130 No. 32 1150 3300 4.1 −7.2 11.2 170 No. 331150 3350 3.8 −7.5 11.5 150

TABLE 5 Rate of change of Firing Dielectric Dielectric loss dielectricconstant temperature constant tan δ with temperature Resistivity Meanfailure time Sample (° C.) (ε_(r)) (%) (%) (ρ:Ωm) (hour) No. 34 11503310 3.5 −9.0 11.4 160 No. 35 1150 3120 3.2 −9.6 11.3 150 No. 36 11753050 4.5 −9.1 11.1 110 No. 37 1175 3200 4.1 −8.5 11.3 130 No. 38 11503300 3.5 −8.1 11.2 150 No. 39 1150 3350 3.1 −7.5 11.4 150 No. 40 11003500 3.8 −8.1 11.1 130 No. 41 1100 3320 3.7 −8.5 11.1 115 No. 42 11503380 4.1 −7.1 11.5 110 No. 43 1150 3350 4.0 −7.5 11.4 115 No. 44 11503370 3.5 −7.8 11.4 120 No. 45 1150 3250 3.1 −8.5 11.3 150 No. 46 11503100 3.8 −8.8 11.1 210 No. 47 1150 3050 4.5 −9.5 11.1 230 No. 48 11503310 4.3 −8.3 11.4 110 No. 49 1150 3070 3.5 −9.1 11.2 170 No. 50 11503290 4.2 −8.5 11.5 115 No. 51 1150 3090 3.2 −9.2 11.3 185 No. 52 11503300 4.1 −7.7 11.4 120 No. 53 1150 3100 3.3 −9.6 11.1 190 No. 54 11503450 4.2 −8.0 11.3 120 No. 55 1175 3210 3.3 −9.4 11.2 195 No. 56 11503300 4.3 −8.1 11.4 110 No. 57 1150 3100 3.2 −9.1 11.1 220 No. 58 11503330 4.1 −7.8 11.5 115 No. 59 1150 3060 3.5 −9.2 11.1 240 No. 60 11503320 4.3 −7.7 11.3 115 No. 61 1150 3050 3.1 −9.6 11.1 190 No. 62 11503310 4.4 −7.8 11.4 110 No. 63 1150 3050 3.1 −9.2 11.1 180 No. 64 11503380 4.5 −7.5 11.5 120 No. 65 1150 3120 3.0 −9.4 11.1 185 No. 66 11503450 4.2 −7.9 11.4 110 No. 67 1150 3110 3.1 −9.1 11.1 200 No. 68 11503450 4.3 −7.7 11.5 115 No. 69 1150 3100 3.2 −9.5 11.1 195

A silver paste containing a B₂O₃—SiO₂—BaO-based glass frit was appliedto both ends of the fired laminate and baked at 600° C. in an N₂atmosphere to form external electrodes each electrically connected tothe internal electrode. Thereby, a laminated ceramic capacitor includingthe dielectric ceramic composition of the present invention wasobtained.

Outer dimensions of each of the resulting laminated ceramic capacitors(sample Nos. 1 to 69) were 5.0 mm in width, 5.7 mm in length, and 2.4 mmin thickness. The thickness of each of the dielectric ceramic layers was1.0 μm. The number of effective dielectric ceramic layers was 5 layers.The area of each of the facing electrodes was 16.3×10⁻⁶ m² per layer.

Next, electrical characteristics, which indicate the performance of thelaminated ceramic capacitor, of sample Nos. 1 to 69 were measured.

Capacitance C and dielectric loss tan δ were measured with an automaticbridge measurement according to JIS 5102. Dielectric constant fr wascalculated from the resulting capacitance C. Tables 4 and 5 show theresults.

To measure insulation resistance IR, an insulation resistance tester wasused. That is, 4 V DC was applied for 1 minute, and insulationresistance IR was measured at +25° C., and then resistivity p wascalculated. Tables 4 and 5 show the results as log ρ.

With respect to the rate of change of capacitance C with temperature,the rate of change ΔC/C_(20° C.) in the range of −25° C. to +85° C. withreference to the capacitance at 20° C. was determined. Tables 4 and 5show the results as the rate of change of the dielectric constant withrespect to temperature.

With respect to a high-temperature load test, 10 V DC was applied at150° C., and the change in insulation resistance IR with time wasmeasured. In the high-temperature load test, the state in which theinsulation resistance IR of each sample reached 10⁵ Ω or less wasdefined as failure. After a time required for reaching the failure wasmeasured, a mean failure time was determined. Tables 4 and 5 show theresults.

As is clear from the measurement results shown in Tables 4 and 5, anyone of the laminated ceramic capacitors (sample Nos. 13 to 69), eachincluding the dielectric ceramic composition having the compositionwithin the range of the present invention, was found to be a highlyreliable laminated ceramic capacitor having a mean failure time of 100hours or more in the high-temperature load test, a high dielectricconstant ε_(r) of 3,000 or more, a small dielectric loss tan δ of 5% orless, a rate of change of the dielectric constant meeting the Bproperties (within ±10%), and a high resistivity ρ of 10¹¹ Ωm (a log ρof 11) or more, in spite of the fact that the thickness of thedielectric ceramic layer was reduced to about 1 μm.

Furthermore, as is clear from the case of sample Nos. 66 to 69, when theamount d, which was the total of the molar ratios of the oxides of tworare-earth elements, was within the range of 0.05≦d≦2.5 relative to 100of (Ba,Ca)TiO₃, it was possible to obtain a laminated ceramic capacitorhaving satisfactory electrical characteristics in the same way as forsample Nos. 13 to 65, even when the thickness of the dielectric ceramiclayer was reduced to about 1 μm.

In contrast, as is clear from the measurement results of sample Nos. 1to 12 shown in Table 4, it was found that if any one of contents of theoxides was outside the limited range of the present invention, theresulting laminated ceramic capacitor had degraded performance even ifeach of the contents of the other oxides was within the limited range ofthe present invention, as described below.

In the case of sample No. 1 using powder A in which Ba ions in(Ba_(1-x)Ca_(x))_(m)TiO₃ were partially replaced with Ca ions and thesubstitution rate x of Ca ions was less than 0.04, the mean failure timein the high-temperature load test was 20 hours, which was very short. Inthe case of sample No. 2 using powder B in which the substitution rate xexceeded 0.20, the dielectric constant ε_(r) was disadvantageously2,700, which was lower than 3,000, the rate of change of the dielectricconstant with respect to temperature was disadvantageously −11.1%, andthe mean failure time was 40 hours, which was short.

In the case of sample No. 3 using powder C in which the ratio m, i.e.,Ba_(1-x)Ca_(x)/Ti, was less than 0.990, the logarithm of resistivity was9.3, i.e., the resistivity was lower than 10¹¹ Ωm, and the mean failuretime could not be measured, which was terrible. In the case of sampleNo. 4 using powder D in which the ratio m exceeded 1.03, the dielectricconstant ε_(r) was 2,400, which was worse than 3,000, the dielectricloss tan δ was 12.5%, which was lower than 5%, the rate of change of thedielectric constant with respect to temperature was −12.8%, which wasworse than ±10%, and the mean failure time could not be measured, whichwas terrible.

In the case of sample No. 5 in which the molar ratio a of MnO was lessthan 0.01 relative to 100 of (Ba_(1-x)Ca_(x))_(m)TiO₃, the resistivitywas lower than 10¹¹ Ωm, and the mean failure time could not be measured,which was terrible. In the case of sample No. 6 in which the molar ratioa exceeded 5, the rate of change of the dielectric constant with respectto temperature was −12.1%, which was worse than ±10%, the resistivitywas lower than 10¹¹ Ωm, and the mean failure time was 20 hours, whichwas very short.

In the case of sample No. 7 in which the molar ratio b of CuO was lessthan 0.05, the mean failure time was 10 hours, which was very short. Inthe case of sample No. 8 in which the molar ratio b exceeded 5, the rateof change of the dielectric constant with respect to temperature was−12.3%, which was worse than ±10%.

In the case of sample No. 9 in which the molar ratio c of SiO₂ was lessthan 0.2, the dielectric constant was 2,400, which was low, thedielectric loss tan δ was greater than 7.8%, the rate of change of thedielectric constant with respect to temperature was −12.5%, which waspoor, and the mean failure time was 15 hours, which was very short. Inthe case of sample No. 10 in which the molar ratio c exceeded 8, therate of change of the dielectric constant with respect to temperaturewas −11.8%, which was poor, and the mean failure time was 40 hours,which was short.

In the case of sample No. 11 in which the molar ratio d of Re₂O₃ wasless than 0.05, the mean failure time was 5 hours, which was very short.In the case of sample No. 12 in which the molar ratio d exceeded 2.5,the rate of change of the dielectric constant with respect totemperature was −11.2%, which was poor.

The present invention is not limited to the above-described examples. Itis understood that various changes may be made without departing fromthe spirit of the invention. For example, at least one rare-earthelement selected among a plurality of types of rare-earth elements isused. When a plurality of types of rare-earth elements are used, thetotal amount d of the molar ratios of oxides of the plurality of typesof the rare-earth elements should satisfy the relationship: 0.05≦d≦2.5.

According to the first to third aspects of the present invention, it ispossible to provide a dielectric ceramic composition and a laminatedceramic capacitor having a high dielectric constant of 3,000 or more, asmall dielectric loss of 5% or less, a temperature characteristic of thedielectric constant meeting the B properties, a high resistivity of 10¹¹Ωm or more, and high reliability, i.e., a mean failure time of 100 hoursor more in an accelerated reliability test (150° C., DC field strength:10 V/μm), even when the thickness of the dielectric ceramic layer isreduced to about 1 μm.

INDUSTRIAL APPLICABILITY

The present invention can be appropriately applied to produce adielectric ceramic composition and a laminated ceramic capacitor.

1. A dielectric ceramic composition represented by the chemicalcomposition formula: 100(Ba_(1-x)Ca_(x))_(m)TiO₃+aMnO+bCuO+cSiO₂+dRe₂O₃wherein coefficients 100, a, b, c, and d each represent a molar amount;Re represents at least one element selected from Y, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, and Yb, and wherein m, x, a, b, c, and d satisfy therespective relationships: 0.990≦m≦1.030, 0.04≦x≦0.20, 0.01≦a≦5,0.05≦b≦5, 0.2≦c≦8, and 0.05≦d≦2.5.
 2. A laminated ceramic capacitorcomprising: a plurality of laminated dielectric ceramic layers; at leasttwo internal electrodes, each being disposed between a different pair ofadjacent dielectric ceramic layers; and at least two external electrodeseach of which is electrically connected to a different internalelectrodes, wherein the dielectric ceramic layers comprise thedielectric ceramic composition according to claim
 1. 3. The laminatedceramic capacitor according to claim 2, wherein each of the internalelectrodes comprises at least one conductive material selected from thegroup consisting of nickel, a nickel alloy, copper, and a copper alloy.4. The dielectric ceramic composition according to claim 1, wherein0.992≦m≦1.027, 0.042≦x≦0.19, 0.1≦a≦4.8, 0.055≦b≦4.7, 0.25≦c≦7.8, and0.055≦d≦2.45.
 5. The dielectric ceramic composition according to claim1, wherein 1.001≦m≦1.011, 0.08≦x≦0.17, 0.2≦a≦3.5, 0.1≦b≦2.5, 0.5≦c≦6,and 0.2≦d≦1.5.
 6. The dielectric ceramic composition according to claim1, wherein m is 1.001, x is 0.08, a is 0.2, b is 0.4, and c is
 2. 7. Alaminated ceramic capacitor comprising: a plurality of laminateddielectric ceramic layers; at least two internal electrodes, each beingdisposed between a different pair of adjacent dielectric ceramic layers;and at least two external electrodes each of which is electricallyconnected to a different internal electrodes, wherein the dielectricceramic layers comprise the dielectric ceramic composition according toclaim
 6. 8. The laminated ceramic capacitor according to claim 7,wherein each of the internal electrodes comprises at least oneconductive material selected from the group consisting of nickel, anickel alloy, copper, and a copper alloy.
 9. A laminated ceramiccapacitor comprising: a plurality of laminated dielectric ceramiclayers; at least two internal electrodes, each being disposed between adifferent pair of adjacent dielectric ceramic layers; and at least twoexternal electrodes each of which is electrically connected to adifferent internal electrodes, wherein the dielectric ceramic layerscomprise the dielectric ceramic composition according to claim
 5. 10.The laminated ceramic capacitor according to claim 9, wherein each ofthe internal electrodes comprises at least one conductive materialselected from the group consisting of nickel, a nickel alloy, copper,and a copper alloy.
 11. A laminated ceramic capacitor comprising: aplurality of laminated dielectric ceramic layers; at least two internalelectrodes, each being disposed between a different pair of adjacentdielectric ceramic layers; and at least two external electrodes each ofwhich is electrically connected to a different internal electrodes,wherein the dielectric ceramic layers comprise the dielectric ceramiccomposition according to claim
 4. 12. The laminated ceramic capacitoraccording to claim 11, wherein each of the internal electrodes comprisesat least one conductive material selected from the group consisting ofnickel, a nickel alloy, copper, and a copper alloy.
 13. The dielectricceramic composition according to claim 1, wherein Re is at least 2 ofsaid elements.
 14. A laminated ceramic capacitor comprising: a pluralityof laminated dielectric ceramic layers; at least two internalelectrodes, each being disposed between a different pair of adjacentdielectric ceramic layers; and at least two external electrodes each ofwhich is electrically connected to a different internal electrodes,wherein the dielectric ceramic layers comprise the dielectric ceramiccomposition according to claim
 13. 15. The laminated ceramic capacitoraccording to claim 14, wherein each of the internal electrodes comprisesat least one conductive material selected from the group consisting ofnickel, a nickel alloy, copper, and a copper alloy.